1. Field of the Invention
The present invention relates generally to a portable terminal with a ground unit, and in particular, to a portable terminal with a variable ground unit configured to reduce a Specific Absorption Rate (SAR) by achieving an optimum ground area corresponding to an open/closed state of the terminal and a mode change thereof, and to contribute to improving radiation performance of an antenna.
2. Description of the Related Art
As the electronic communications industry is developed, a portable terminal is becoming smaller and slimmer while providing more various functions. For example, a portable terminal is provided with a speaker unit that can implement various melodies and chords, and a color display unit having millions of pixels. Besides a basic communications function, the terminal may provide an MP3 player function, game contents using the display unit, and a Digital Multimedia Broadcast (DMB) function for providing a public broadcasting service.
Various types of terminals are being continuously released to meet users' demands. In general, the terminals may be classified according to how the terminal is opened or closed for a calling function of the terminal. Thus, the terminal may be classified into a basic bar type, a flip type, a folder type, a slide type, a pop-up type, a slide and rotation type.
Each of the aforementioned terminals includes a predetermined ground unit. The ground unit is formed at a main board in general, and may serve as a conductor for electronic function groups installed on the main board, or as a conductor for a smooth operation of an antenna radiator for wireless communications. Also, the ground unit may be extended to shield an electronic wave potentially harmful to the human body.
Since the terminals are used as portable wireless devices, a predetermined antenna is provided to each of the terminals. Various types of antennas are being used for the terminals. Examples of the antennas may include an external antenna unit protruding outside the terminal, and a built-in antenna so-called ‘intenna’ mounted inside the terminal. The antenna must be disposed at a proper place of the terminal to maximize its performance, depending on the type of opening and closing a sub-body of the terminal. For example, in the folder type terminal and the slide type terminal, a terminal performs its antenna function by an external antenna protruding upwardly from a main body, or by an internal antenna radiator at a predetermined rear surface inside the main body.
However, since the terminals are designed in a stand-off type such that the optimum antenna coupling is performed when the sub-body is opened or closed, or an intermediate radiation characteristic is obtained, thereby resulting in degradation in overall radiation characteristic of the terminal. Also, the radiation characteristic may degrade because of a finger touch occurring when a user grabs the terminal for calling.
Therefore, the terminals include a separate ground unit. For example, in the case of the folder type terminal or the slide type terminal including a hinge module or a slide hinge module that mechanically connects a main body with a folder or a slide body, the hinge module is electrically connected to a ground layer of a main board installed in the main body, thereby expanding a ground layer. This serves to shield an electronic wave, thereby minimizing bad influence of the terminal on the human body.
When the folder or the slide body is opened for a calling operation, the above-mentioned structure, in which a ground layer of the main board of the main body is grounded uniformly with a ground layer of the hinge module or of the hinge module and the sub-body, reduces influence on the human body and improves radiation efficiency of the antenna. However, the radiation efficiency of the antenna degrades on the free space because of the expansion of the ground area.
Also, the terminal includes one or more antennas having integral or individual functions operating within different frequency bands in response to the current tendency of making a terminal cover various bands of, for example, Code Division Multiple Access (CDMA), a Digital Cellular System (DCS), a Personal Communications System (PCS), Digital Multimedia Broadcasting (DMB), and Bluetooth®. The antennas of different bands are different in ground area for the optimum operation.
Therefore, a portable terminal requires a variable ground unit that can perform optimum antenna coupling depending on an opened/closed state of the sub-body, or a corresponding band among multiple bands.